action_tutorials_py

Python action tutorial code

README

Action Server

In the constructor for FibonacciActionServer, an action server is created with a callback that is called when a goal is accepted.

self._action_server = ActionServer(
            self,
            Fibonacci,
            'fibonacci',
            self.execute_callback)

There are three types of callbacks:

  • A goal_callback can optionally be added to conditionally accept or reject the goal, however, by default the goal is accepted.

  • A cancel_callback can also optionally be added to conditionally accept or reject the cancel goal request, however, by default the cancel goal request is accepted.

  • The execute_callback calculates the Fibonacci sequence up to order and publishes partial sequences as feedback as each item is added to the sequence.

The thread sleeps for 1 second between the calculation of each item in order to represent a long-running task. When execution is complete, the full sequence is returned to the action client.

Action Client

In the constructor for FibonacciActionClient, an action client for the fibonacci action is created:

self._action_client = ActionClient(self, Fibonacci, 'fibonacci')

A goal of type Fibonacci is created with order 10. The goal is sent asynchronously with callbacks registered for the goal response and the feedback:

self._send_goal_future = self._action_client.send_goal_async(
            goal_msg,
            feedback_callback=self.feedback_callback)

self._send_goal_future.add_done_callback(self.goal_response_callback)

Within the goal_response_callback, if the goal is accepted, the goal result is requested asynchronously. A callback is registered for receiving the result:

self._get_result_future = goal_handle.get_result_async()

self._get_result_future.add_done_callback(self.get_result_callback)

There are two types of callbacks:

  • The feedback_callback logs the partial sequences as they are received.

  • The get_result_callback logs the full Fibonacci sequence.